The invention concerns a method for manufacturing lamination packs in a tool for punching laminations onto which laminations glue is applied and which laminations are assembled to a lamination pack. The invention also concerns a tool for producing lamination packs according to said method and an apparatus for producing lamination packs according to said method.
Electrical machines often use cores of stacked laminations that are manufactured from cut electrical sheets. Typically, a punching press is used in order to cut the individual laminations. The manufacture of the core or of the pack can be done in several ways, including mechanical joining of the parts in the press for forming the cores, welding, gluing, or mechanical joining of the laminations into packs outside of the press.
Examples of prior patents in the field of manufacturing packs outside of tool and press are disclosed in GB 1 501 676. This reference discloses how packs of steel having a heat-activated coating are produced. U.S. Pat. No. 4,538,345 discloses as a solution a process in which the laminations are provided with projections and depressions by means of which the laminations are compressed to form the pack. This so-called interlocking process has several disadvantages:    (a) The interlocking technique requires manufacture of very complex tools whose parts are very sensitive with regard to material quality and are less robust than tools not to be used for interlocking laminations. This increases the costs as well as the risks associated with the method; this may diminish its usefulness.    (b) Very thin sheet steel, for example, less than 0.35 mm thick, is difficult to interlock and this leads to low efficiency methods.    (c) Some products require that each lamination be rotated by a certain amount. In the case of a pack whose laminations are to be interlocked the angle of rotation is limited by the number of existing interlocking locations, i.e., in the case of four existing interlocking locations the smallest possible angle of rotation is 90 degrees.    (d) A further disadvantage of the present interlocking technique resides in that materials of different thickness or properties (often characterized by different quality specifications) cannot be joined.
Other techniques that employ an externally applied adhesive have also been tried. DE 35 35 573 and DE 203 18 993 are examples therefore and both disclose a method for employing an adhesive that is applied onto the strip surface. The utilization of capillary gluing, i.e., allowing a glue “seam” to run down an outer edge of the pack, has also been tried.
Various problems are associated with the various existing techniques for applying an adhesive onto the strip surface when used as an integral part of the core manufacture.    (a) The possible press speeds are limited by the speed of application of the adhesive. For example, DE 203 18 993 defines speed ranges up to 200-300 strokes per minute. For an inexpensive core production, the press speeds must be at least at 400 strokes per minute; typically, values of above 600 strokes per minute are very desirable.    (b) It is difficult to keep the tool clean. For example, in one of the techniques a batch size limit of a few thousand strokes is probable; thereafter, the tool must be serviced and cleaned. The normal servicing interval for a carbide tool is a minimum of 2,000,000 strokes. Shorter operating times drive up the production costs significantly.    (c) Existing systems as disclosed in DE 20 31 899 are known to have problems in regard to wear of the parts.    (d) The packs that are produced by means of some adhesive techniques can have variable/unreliable strengths of the pack.    (e) The cost of tools with integrated application units can be significantly higher than the cost of standard tools.    (f) The technology of an application system integrated into a tool can normally not be used in connection with already existing tools.
Items (a), (b), and (c) all relate to the fact that the application of the adhesive is based on contact between the application unit and the strip.
An advantage provided by gluing relative to other joining technologies resides in that between the laminations in a pack there is no electrical contact. With techniques such as interlocking or welding a contact is produced. This increases possible loss in the completed motor, in particular at high frequencies. A reliable gluing method would have two benefits: Either the efficiency of the motor is improved for a given pack size or a smaller motor could be used to achieve the same output as a larger pack that is welded or interlocked or manufactured by another contacting joining method.
Another problem that can occur during punching of the lamination parts is the release of pieces of material, often referred to as “scrap metal”, that fall back into the cutting area of the tool. This can cause the tool to be damaged; in turn, this leads to downtime when the tools must be repaired.